The present invention relates to an inflator, and more particularly relates to an inflator for an air-bag intended for use in a motor vehicle such as a motor car.
It has been proposed previously to provide an air-bag mounted in a motor vehicle, the air-bag being adapted to be inflated in the event that an accident should occur so that the air-bag, when inflated, is located in front of the occupant of the vehicle to provide protection for the occupant of the vehicle.
Various techniques have been used to prevent injuries being caused by the impact between the air-bag and the occupant of a seat, which can happen if the airbag inflates very abruptly or very aggressively. For example, it has been proposed to provide venting holes or valves associated with the air-bag so that high pressure gas may be vented from the interior of the air-bag. Alternatively it has been proposed that the air-bag may be inflated in two or more stages following an impact situation.
A recently developed two-stage inflation technique uses a gas mixture containing mainly inert gas and a small amount of flammable gas. The gas is introduced into the air-bag, thus commencing inflation of the air-bag, and finally the flammable gas is ignited, with a result that the total gas content within the air-bag expands, inflating the air-bag to a desired final pressure.
To prevent the unintentional premature ignition of the flammable gas, it has been proposed that an oxidisable gas, such as a fuel gas, should be stored in one gas chamber, and a gas such as oxygen, should be stored in a separate gas chamber. It is only when gas from the two chambers has been introduced into the interior of the air-bag, and mixed, that the flammable gas exists.
U.S. Pat. No. 5,820,161 discloses an arrangement of this type.
For an air-bag of this type to operate in a satisfactory manner, both of the gas chambers must be opened simultaneously, and the resultant gas mixture in the airbag must be ignited after a specified time delay. Non-simultaneous opening of the chambers and/or a time delay of an inappropriate time period, may lead to incomplete combustion, delayed ignition, or in a worse case, no ignition at all of the gas mixture.
The present invention seeks to provide an improved inflator.
According to this invention there is provided an inflator for an air-bag, the inflator comprising a first gas chamber for containing a first gas, and second gas chamber for containing a second gas, each gas chamber being mounted on a central block or housing, the central block or housing defining gas flow passages leading from each gas chamber to direct gas to an air-bag. Each passage is initially closed by a closure, the housing containing an opening element associated with each closure, adapted to move from an initial position in which integrity of the closure is maintained to a final position in which the closure is opened. There is an igniter to generate hot gas, and an actuating element adapted to be moved in response to the generation of the hot gas, means being provided to constrain the actuating element to move in a predetermined direction over at least part of its movement. The actuating element acts upon the opening elements to move the opening elements substantially simultaneously to open the closure elements to permit (1) gas to flow from the gas chambers through the gas ducts, (2) movement of the actuating element and the opening elements over a predetermined distance, and (3) opening a further gas flow path to permit gas from the igniter to flow through the gas ducts.
In operation of an embodiment of the invention the gas from the ignitor, when it has flowed through the said gas ducts, will ignite the mixed first and second gases.
Preferably the central block or housing defines two passages, each passage extending from a central part of the block or housing, to a respective closure, each passage containing a respective opening element, the actuating element being adapted, on movement in response to the generation of hot gas, to engage and act on part of each opening element to cause the opening elements to move substantially simultaneously to open the closures.
Conveniently each opening element comprises a head defining an end face and wherein the actuating element includes surfaces adapted to engage with said end faces, either the end faces or the surfaces, or both the end faces and the surfaces, being inclined with respect to the axes of the passages to provide a wedging effect.
Preferably the head of each opening element is provided with an inclined planar face, and the actuating element is of substantially conical form.
Conveniently the conical surface of the actuating element is provided with a plurality of cut-outs.
Advantageously the actuating element is provided with an axially extending skirt, the axially extending skirt initially being received in an annular passage, the skirt and the annular passage co-operating to constrain the actuating element to move in said predetermined direction.
Preferably a separate respective gas flow duct is provided extending from each said passage to form a gas flow path from the passage to the interior of the airbag.
Advantageously the first gas chamber contains an oxidisable gas, alone or in admixture with an inert gas, and wherein the second gas chamber contains an oxidising gas, alone or in combination with an inert gas. The oxidisable gas may be methane, ethane, propane, acetylene, hydrogen or mixtures thereof. The oxidising gas may be oxygen or an oxide of nitrogen. The inert gas may be argon or helium or a mixture thereof.
Conveniently each closure is in the form of a breakable foil.